U.S. patent application number 10/575401 was filed with the patent office on 2008-10-09 for steering control apparatus and method.
This patent application is currently assigned to nissan Motor Co., Ltd.. Invention is credited to Takaaki Eguchi, Kazuo Hara.
Application Number | 20080249685 10/575401 |
Document ID | / |
Family ID | 36588249 |
Filed Date | 2008-10-09 |
United States Patent
Application |
20080249685 |
Kind Code |
A1 |
Hara; Kazuo ; et
al. |
October 9, 2008 |
Steering Control Apparatus and Method
Abstract
A vehicle steering controller includes a turning unit which is
mechanically separated from a steering unit, which receives the
steering input, and turns the road wheels corresponding to the
steering input. The controller also includes a reaction force motor
that applies a steering reaction force corresponding to the turning
state of the turning unit to the steering unit, a hands-off
detection sensor that detects whether the steering unit is in the
hands-off state, and a steering reaction force correction component
that reduces the steering reaction force from that in the hands-on
state when the hands-off state is detected.
Inventors: |
Hara; Kazuo; (Kanagawa,
JP) ; Eguchi; Takaaki; (Kanagawa, JP) |
Correspondence
Address: |
YOUNG & BASILE, P.C.
3001 WEST BIG BEAVER ROAD, SUITE 624
TROY
MI
48084
US
|
Assignee: |
nissan Motor Co., Ltd.
Kanagawa
JP
|
Family ID: |
36588249 |
Appl. No.: |
10/575401 |
Filed: |
December 13, 2005 |
PCT Filed: |
December 13, 2005 |
PCT NO: |
PCT/IB2005/003770 |
371 Date: |
April 10, 2006 |
Current U.S.
Class: |
701/42 |
Current CPC
Class: |
B62D 5/0466 20130101;
B62D 5/006 20130101; B62D 6/008 20130101 |
Class at
Publication: |
701/42 |
International
Class: |
B62D 6/04 20060101
B62D006/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 14, 2004 |
JP |
2004-361986 |
Claims
1. A steering control device for use in a vehicle having a steering
wheel that receives steering input, and an
electronically-controlled steering unit that turns the vehicle's
wheels over a road surface based on the position of the steering
wheel, comprising: a reaction force device coupled to the steering
wheel and responsive to a control signal to apply a steering
reaction force to the steering wheel; a hands-free sensor adapted
to generate a signal indicative of whether the steering wheel is in
a hands-on state or a hands-off state; and a controller adapted to
vary the control signal in response to the hands-free sensor signal
to reduce the steering reaction force applied when the hands-off
state is indicated relative to the steering reaction force applied
when the hands-on state is indicated.
2. The steering control device of claim 1, further comprising: a
road surface reaction force sensor adapted to generate a signal
indicative of road surface reaction force, wherein the reaction
force device is further adapted to apply the steering reaction
force corresponding to the indicated road surface reaction force;
and wherein the controller is further adapted to reduce the
steering reaction force corresponding to the indicated road surface
reaction force when the hands-off state is indicated.
3. The steering control device of claim 1, further comprising a
steering angle detection sensor adapted to generate a signal
indicative of the steering angle of the steering wheel; wherein the
steering reaction force device is further adapted to apply a
steering reaction force corresponding to the steering angle; and
wherein the controller is further adapted to reduce the reaction
force corresponding to the indicated steering angle when the
hands-off state is indicated.
4. The steering control device of claim 1, further comprising a
steering angle acceleration detection sensor adapted to generate a
signal indicative of the steering angle acceleration; wherein the
steering reaction device applies a steering reaction force
corresponding to the indicated steering angle acceleration; and
wherein the controller is further adapted to reduce the reaction
force corresponding to the indicated steering angle acceleration
when the hands-off state is indicated.
5. The steering control device of claim 1, further comprising a
steering angle velocity detection sensor adapted to generate a
signal indicative of the steering angle velocity; wherein the
steering reaction device applies a steering reaction force
corresponding to the indicated steering angle velocity; and wherein
the controller is further adapted to reduce the reaction force
corresponding to the indicated steering angle velocity when the
hands-off state is indicated.
6. The steering control device of claim 1, further comprising a
steering torque detection sensor adapted to generate a signal
indicative of steering torque; and wherein the controller is
further adapted to reduce the reaction force when the indicated
steering torque decreases and the hands-off state is not
indicated.
7. A vehicle having road wheels, comprising: a steering unit; an
electronically-controlled turning unit responsive to the steering
unit which turns the road wheels based on the position of the
steering unit; a steering reaction force applicator adapted for
applying a steering reaction force to the steering unit; a
hands-free sensor adapted for detecting whether the steering unit
is in a hands-off state or a hands-on state; and a steering
reaction force correction component adapted for reducing the
steering reaction force applied when the hands-off state is
detected relative to the steering reaction force applied when the
hands-on state is detected.
8. The vehicle of claim 7, further comprising: a road surface
reaction force sensor adapted for detecting the road surface
reaction force; wherein the steering reaction force applicator
applies a steering reaction force corresponding to the road surface
reaction force; and wherein the steering reaction force correction
component reduces the steering reaction force corresponding to the
road surface reaction force when the steering unit is in the
hands-off state.
9. The vehicle of claim 7, further comprising a steering angle
detection sensor for detecting the steering angle of the steering
wheel; wherein the steering reaction force applicator applies a
steering reaction force corresponding to the steering angle; and
wherein the steering reaction force correction component reduces
the steering reaction force corresponding to the steering angles
when the hands-off state is detected.
10. The vehicle of claim 7, further comprising a steering angle
acceleration detection sensor for detecting the steering angle
acceleration; wherein the steering reaction force applicator
applies a steering reaction force corresponding to the steering
angle acceleration; and wherein the steering reaction force
correction component reduces the steering reaction force
corresponding to the steering angles when the hands-off state is
detected, but reference steering angle acceleration.
11. The vehicle of claim 7, further comprising a steering angle
velocity detection sensor adapted for detecting the steering angle
velocity; wherein the steering reaction force applicator applies a
steering reaction force corresponding to the steering angle
velocity, and wherein the steering reaction force correction
component reduces the steering reaction force corresponding to the
steering angle velocity when the hands-off state is detected.
12. The vehicle of claim 7, further comprising a steering torque
detection sensor adapted for detecting steering torque; wherein the
steering reaction force correction component reduces the steering
reaction force when the steering torque becomes smaller if the
hands-off state is not detected.
13. A vehicle for controlling road wheels of the vehicle
comprising: means for turning the road wheels in response to a
steering input of a steering unit; means for applying a steering
reaction force to the steering unit; means for detecting whether
the steering unit is in a hands-on or hands-off state; and means
for reducing the steering reaction force in the hands-on state when
the hands-off state is detected.
14. A method for controlling the road wheels of a vehicle
comprising: turning the road wheels from a steering input via a
steering unit; applying a steering reaction force to the steering
unit; detecting whether the steering unit is in a hands-on or
hands-off state; and reducing the steering reaction force applied
when the hands-off state is detected relative to the steering
reaction force applied when the hands-on state is detected.
15. The method of claim 14, further comprising; detecting a road
surface reaction force; applying a steering reaction force to the
steering unit corresponding to the road surface reaction force; and
reducing the steering reaction force corresponding to the road
surface reaction force when the hands-off state is detected.
16. The method of claim 14, further comprising: detecting the
steering angle; applying the steering reaction force to the
steering unit corresponding to the steering angle; and reducing the
steering reaction force corresponding to the steering angle when
the hands-off state is detected.
17. The method of claim 14, further comprising: detecting the
steering angle acceleration; applying the steering reaction force
to the steering unit corresponding to the steering angle
acceleration; and reducing the steering reaction force
corresponding to the steering angle acceleration when the hands-off
state is detected.
18. The method of claim 14, further comprising: detecting the
steering angle velocity; applying the steering reaction force to
the steering unit corresponding to the steering angle velocity; and
reducing the steering reaction force corresponding to the steering
angle velocity when the hands-off state is detected.
19. The method of claim 14, further comprising: detecting the
steering torque; applying the steering reaction force to the
turning means corresponding to the steering torque; and reducing
the steering reaction force corresponding to the steering torque
when the hands-off state is detected.
Description
BACKGROUND
[0001] The present invention relates to the field of steering
control for vehicles and in particular to electronic (or
"steer-by-wire") steering control systems.
[0002] In the field of steer-by-wire systems, a steering reaction
force sensor is placed on the tie rod, and the road surface
reaction force detected by the steering reaction force sensor is
added to the steering reaction torque, so that the force acting
from the road surface on the tires is reflected on the steering
reaction force torque.
[0003] In order to reliably transmit the road surface feel to the
driver in a steer-by-wire system, a control value corresponding to
the road surface reaction force is added to the steering reaction
force torque. For example, in the technology described in Japanese
Kokai Patent Application No. Hei 10[1998]-217988, in the steering
force computation unit, on the basis of the detection result of the
steering force sensor, steering force T applied to the steering
shaft is computed. At the same time, control value (aT) for
rotating the steering shaft in the direction of applied steering
force T is computed. In the steering reaction force computation
unit, on the basis of the detection result of the steering reaction
force sensor, steering reaction force F applied to the steering
shaft is computed. In the steering shaft motor controller, on the
basis of these computational results of the steering force
computation unit and steering reaction force computation unit,
rotation control value Mm of the steering shaft is computed using
the following equation, and the reaction force control signal
corresponding to rotation control value Mm is output to steering
shaft motor. In the following equation, Gm represents the gain
coefficient indicating the gain of the output signal.
Mm=Gm*(aT-F)
SUMMARY
[0004] If steering reaction force Mm is set to an appropriate value
for steering, when the hands are released, the steering wheel may
go past the neutral position and overshoot.
[0005] The present invention discloses a vehicle steering
controller for controlling road wheels on a vehicle including a
turning unit which receives steering input and turns the road
wheels in accordance with the steering input, a steering unit
mechanically separated from the turning unit, a steering reaction
force applicator adapted for applying a steering reaction force
corresponding to a turning state of the turning unit on the
steering unit, a hands-free sensor adapted for detecting whether
the steering unit is in a hands-off state or a hands-on state, and
a steering reaction force correction component adapted for reducing
the steering reaction force in the hands-on state when the
hands-off state is detected.
[0006] A method for controlling the road wheels of a vehicle is
also disclosed including turning the road wheels from a steering
input via a turning unit, mechanically separating the turning unit
from a steering unit, applying a steering reaction force
corresponding to a turning state of the turning unit on the
steering unit, detecting whether the steering unit is in a hands-on
or hands-off state, and reducing the steering reaction force in the
hands-on state when the hands-off state is detected.
[0007] In the foregoing, preferred embodiments of the present
invention were explained. However, the present invention is not
limited to the embodiments 1-4. As long as the essence of the
invention is observed, changes may be made to the design of the
present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The description herein makes reference to the accompanying
drawings wherein like reference numerals refer to like parts
throughout the several views, and wherein:
[0009] FIG. 1 is an overall system diagram illustrating the vehicle
steering controller according to the first embodiment;
[0010] FIG. 2 is a flow chart illustrating the setting control
process of a road surface reaction force gain executed by a
controller according to the first embodiment;
[0011] FIG. 3 is a graph used to set a road surface reaction force
coefficient D corresponding to the values of torque sensors on the
steering wheel side;
[0012] FIG. 4 is a graph used to set a steering angle gain
corresponding to a steering angle;
[0013] FIG. 5 is a graph used to set a steering angle acceleration
gain corresponding to a steering angle acceleration;
[0014] FIG. 6 is a graph used to set a steering angle velocity gain
corresponding to a steering angle velocity;
[0015] FIG. 7 is a graph used to set a road surface reaction force
gain corresponding to a road surface reaction force in a hands-on
state;
[0016] FIG. 8 is a graph illustrating with the overshoot problem in
the hands-off state of the earlier technology;
[0017] FIG. 9A is a graph illustrating the steering reaction force
torque with respect to the steering angle in the hands-on
state;
[0018] FIG. 9B is a graph illustrating the steering reaction force
torque with respect to the steering angle in the hands-off
state;
[0019] FIG. 10 is a graph illustrating the process of preventing
overshoot in the hands-off state in the first embodiment;
[0020] FIG. 11 is a flow chart illustrating a control process for
the setting steering angle gain executed by the controller in the
second embodiment;
[0021] FIG. 12 is a graph used to set the steering angle
coefficient in the second embodiment and the steering angle
acceleration coefficient in the third embodiment; and
[0022] FIG. 13 is a graph used to set the steering angle
acceleration coefficient in the fourth embodiment.
DETAILED DESCRIPTION
[0023] In the embodiments disclosed below, it is possible to
provide a reliable road feel to the driver by means of a steering
reaction force torque corresponding to the road surface reaction
force. Also, in the hands-off state, the steering reaction force
torque is set smaller than that in the hands-on state, so that an
appropriate restoration can be effected, thereby avoiding
overshoot.
[0024] FIG. 1 is an overall system diagram illustrating the vehicle
steering controller of the first embodiment. The vehicle steering
controller of the first embodiment includes a steering unit, backup
device, turning unit, and controller.
[0025] The steering unit has a steering angle sensor 1 (means for
detecting the steering angle), an encoder 2, torque sensors 3
(means for detecting the steering torque), and a reaction force
motor 5 (means for applying the steering reaction force).
[0026] The steering angle sensor 1 is a means for detecting the
angular position of steering wheel 6. It is set on column shaft 8a
that bonds cable column 7 and steering wheel 6. That is, steering
angle sensor 1 is placed between steering wheel 6 and torque
sensors 3 and is unaffected by the change in angle due to the
twisting of torque sensors 3, so that it can detect the steering
angle. In the steering angle sensor 1, an absolute type resolver
(not shown) or the like is used.
[0027] The torque sensors 3 form a double system and are arranged
between the steering angle sensor 1 and the reaction force motor 5.
Each torque sensor 3 has a torsion bar extending in the axial
direction, a first shaft connected to one end of the torsion bar
and coaxial to the torsion bar, a second shaft connected to the
other end of the torsion bar and coaxial to the torsion bar and the
first shaft, a first magnetic body fixed to the first shaft, a
second magnetic body fixed to the second shaft, a coil facing the
first magnetic body and the second magnetic body, and a third
magnetic body that surrounds the coil and forms a magnetic circuit
together with the first magnetic body and second magnetic body. The
coil detects the torque from the output signal on the basis of the
inductance that changes corresponding to the relative displacement
between the first magnetic body and the second magnetic body on the
basis of the twisting of the torsion bar.
[0028] The reaction force motor 5 is a reaction force actuator that
imparts a reaction force to steering wheel 6. It is made of a
1-rotor/1-stator type electric motor with the column shaft 8a as
the rotary shaft. Its housing is fixed at an appropriate location
of the vehicle body. A brushless motor is used as the reaction
force motor 5, with encoder 2 and a Hall IC (not shown in the
figure), which are required for use with a brushless motor. Here,
if only a Hall IC is used, although it will still be possible to
drive the motor, nevertheless there will be small variations in the
output torque, and the feel of the steering reaction force will be
poor. In order to effect smoother control of the reaction force,
encoder 2 is placed on the shaft of column shaft 8a to control the
motor. As a result, the small torque variations can be reduced, and
the steering reaction force feel is improved. Also, a resolver can
be used in place of encoder 2.
[0029] The auxiliary unit is composed of a cable column 7 and a
clutch 9. The clutch 9 is arranged between column shaft 8a and
pulley shaft 8b; an electromagnetic clutch is used in the first
embodiment. After it is engaged, the clutch 9 connects column shaft
8a, the input shaft, to pulley shaft 8b, the output shaft. The
clutch 9 mechanically transmits the steering torque from steering
wheel 6 to steering unit 15.
[0030] The cable column 7 has a mechanical backup mechanism that
can play the part of the column shaft in transmitting torque while
it detours to avoid interference with the element included between
the steering unit and the turning unit in backup state when the
clutch 9 is engaged. In the structure of cable column 7, two
interior cables, each end of which is fixed to a reel, are wound
onto the two reels, and the two ends of the exterior sheath in
which two interior cables are inserted are fixed to two reel
housings.
[0031] The steering unit includes an encoder 10, a steering angle
sensor 11, a torque sensors 12, (means for detecting the road
surface reaction force), steering motors 14, steering unit 15, and
steered road wheels 16, 16'.
[0032] The steering angle sensor 11 and torque sensors 12 are
mounted on pinion shaft 17, on one end of which the pulley of cable
column 7 is attached, and on the other end of which a pinion gear
is formed. As steering angle sensor 11, an absolute type resolver
or the like, which detects the rotational velocity of the shaft,
can be used. Also, like the torque sensors 3, torque sensors 12,
form a double system that detects torque from changes in
inductance. Then, steering angle sensor 11 is set on the side of
cable column 7, and torque sensors 12 are set on the side of
steering unit 15. As a result, when the steering angle is detected
by steering angle sensor 11, it is unaffected by the change in the
angle due to the twisting of torque sensors 12.
[0033] The steering motors 14, have a structure in which a pinion
gear engaged to the worm gear set at the central position between
steering angle sensor 11 of the pinion shaft 17 and torque sensors
12, is set on the motor shaft, so that a steering torque is applied
to pinion shaft 17 when the motor is ON. The steering motors 14,
form a double system with a 1-rotor/2-stator structure. They are
brushless motors that form first steering motor 14 and second
steering motor 14. Also, similar to the reaction force motor 5, due
to the adoption of the brushless motors, encoder 10 and a Hall IC
(not shown in the figure) is used.
[0034] The steering unit 15 has a structure in which left/right
steered road wheels 16 turn as pinion shaft 17 rotates. It has rack
shaft 15b that forms a rack gear engaged with the pinion gear of
pinion shaft 17 and inserted in rack tube 15a, tie rods 15c, 15c'
fixed to the two ends of rack shaft 15b extending in the left/right
direction of the vehicle, and knuckle arms 15d, 15d' having one end
fixed to the tie rods 15c, 15c' and the other end fixed to steered
wheels 16, 16'.
[0035] The controller has a double system structure composed of two
controllers 19, 19' that perform processing and arithmetic
operations with two power sources 18, 18'.
[0036] The controller 19 receives the detected signals from the
following parts: steering angle sensor 1, encoder 2, torque sensors
3, and the Hall IC of the reaction force device, as well as the
encoder 10, steering angle sensor 11, torque sensors 12, Hall IC,
and vehicle speed sensor 21 of the steering device.
[0037] On the basis of the detection values of the various sensors,
controller 19 sets the control values of reaction force motor 5 and
steering motor 14, and controls and drives each of steering motors
14. Also, during ordinary system conditions, controller 19 releases
clutch 9. Otherwise, the system engages clutch 9 to establish a
mechanical connection between steering wheel 6 and steered wheels
16, 16'.
[0038] Setting the reaction force motor control value is discussed
hereinafter. In controller 19, the following Equation 1 is used to
set control value Th of the reaction force motor 5.
Th=Kp.times.0+Kd.times.d0/dt+Kdd.times.d.sup.20/dt.sup.2+D.times.Kf.time-
s.F (1)
[0039] Here, .theta. represents the steering angle, Kp represents
the steering angle gain, Kd represents the steering angle velocity
gain, Kdd represents the steering angle acceleration gain, D
represents the road surface reaction force coefficient, and Kf
represents the road surface reaction force gain.
[0040] In Equation 1, the first, second and third terms on the
right-hand side set the control value of the steering reaction
force on the basis of steering angle .theta., and the fourth term
on the right-hand side sets the control value on the basis of road
surface reaction force F, so that it can reflect the influence of
the force acting from the road surface on the tires to the steering
reaction force torque. Also, steering angle acceleration
d.sup.2.theta./d.sup.2t and steering angle velocity d.theta./dt are
computed from the detected value of steering angle sensor 1
(corresponding to the means for detecting the acceleration
computing means and the means for detecting the steering angle
velocity).
[0041] Setting the control value corresponding to the hands-off
state is discussed hereinafter. In Equation 1, road surface
reaction force feedback gain Kf that determines the value of the
reflected steering reaction force torque on the basis of the road
surface reaction force changes value as a function of the steering
state. FIG. 2 is a flow chart illustrating the process flow in
setting and controlling road surface reaction force gain Kf
executed by controller 19 in first embodiment.
[0042] In step S1, the various sensor signals are read, and process
control then goes to step S2. In step S2, from the sensor signals
of torque sensors 3 on the steering wheel side read in step S1, it
is determined whether the system is in the hands-off state (it
corresponds to the hands-off detection means). If YES, it goes to
step S4. If NO, it goes to step S3. Judgment of the hands-off state
is made when the sensor signals of torque sensors 3 are below a
prescribed level. Here, the prescribed value refers to the
hysteresis characteristics of torque sensors 3, and it is set from
the hysteresis range when the torque input corresponds to zero.
[0043] In step S3, because it was determined that the system is not
in the hands-off state in step S2, road surface reaction force gain
Kf is set at prescribed High value (corresponding to the steering
reaction force correction means), and it then returns.
[0044] In step S4, because it was determined that the system is in
the hands-off state in step S2, road surface reaction force gain Kf
is set at prescribed Low value smaller than the High value, and it
then returns.
[0045] In the hands-off state, road surface reaction force gain Kf
is set smaller, and the control value based on road surface
reaction force F is smaller so that an appropriate steering wheel
restoration can be obtained. On the other hand, in the hands-on
state, road surface reaction force gain Kf is set larger and the
control value based on road surface reaction force F is larger so
that an appropriate steering reaction force can be obtained.
[0046] Setting of control value corresponding to the steering
torque in the hands-on state is discussed hereinafter. In Equation
1, in the hands-on state, road surface reaction force coefficient D
that determines the steering reaction force torque based on the
road surface reaction force changes value corresponding to the
steering torque.
[0047] FIG. 3 is a diagram illustrating a graph used to set road
surface reaction force coefficient D corresponding to the value of
torque sensors 3 on the steering wheel side. The road surface
reaction force coefficient D is set such that it has a prescribed
minimum value in the range of the torque sensor value corresponding
to the hands-off state, and it has a larger value when the absolute
value of the torque sensor value becomes larger. Also, in order to
prevent the steering reaction force torque from becoming too large,
when the absolute value of the torque sensor value exceeds a
prescribed level, it becomes a prescribed maximum value.
[0048] Setting of control value corresponding to the steering state
is now discussed. In Equation 1, steering angle gain Kp for setting
the control value of the steering reaction force on the basis of
steering angle .theta. changes as a function of steering angle
.theta.. As shown in FIG. 4, steering angle gain Kp is set such
that it is larger for larger absolute value of steering angle
.theta.. Also, steering angle gain Kp is set to have a larger value
for a higher vehicle speed.
[0049] Also, in Equation 1, steering angle acceleration gain Kdd
for setting the change in the steering reaction force based on
steering angle acceleration d.sup.2.theta./d.sup.2t varies as a
function of steering angle acceleration d.sup.2.theta./d.sup.2t. As
shown in FIG. 5, steering angle acceleration gain Kdd is set such
that it becomes larger when the absolute value of steering angle
acceleration d.sup.2.theta./dt.sup.2 becomes larger. Also, steering
angle acceleration gain Kdd is set such that it is larger when the
vehicle speed is higher.
[0050] Also, in Equation 1, steering angle velocity gain Kd for
setting the control value of the steering reaction force on the
basis of steering angle velocity d.theta./dt changes as a function
of steering angle velocity d.theta./dt. As shown in FIG. 6,
steering angle gain Kd is set such that it is larger for larger
absolute value of steering angle velocity d.theta./dt. Also,
steering angle gain Kd is set to have a larger value for a higher
vehicle speed.
[0051] Setting of control value corresponding to road surface
reaction force is now discussed. In Equation 1, road surface
reaction force gain Kf is not limited to the two values of High and
Low. In addition, it may change as a function of road surface
reaction force F. In this case, road surface reaction force gain Kf
is set such that it is larger when the absolute value of road
surface reaction force F is larger (FIG. 7).
[0052] In conventional steer-by-wire systems, in order to reliably
transmit the road surface feel to the driver, a control value
corresponding to the road surface reaction force is added to the
steering reaction force torque. On the basis of the detection
result of a steering force sensor, steering force T applied to the
steering shaft is computed. At the same time, control value (aT)
for rotating the steering shaft in the direction of applied
steering force T is computed. In the steering reaction force
computation unit, on the basis of the detection result of the
steering reaction force sensor, steering reaction force F applied
to the steering shaft is computed. In the steering shaft motor
controller, on the basis of these computational results of the
steering force computation unit and steering reaction force
computation unit, rotation control value Mm of the steering shaft
is computed using the following equation, and the reaction force
control signal corresponding to rotation control value Mm is output
to steering shaft motor. In the following equation, Gm represents
the gain coefficient indicating the gain of the output signal.
Mm=Gm.times.(a T-F) (2)
[0053] However, in the related art, when steering reaction force Mm
is set to an appropriate value for steering, when the hands are
released, the steering wheel restoration force becomes too large,
so that the steering wheel goes past the neutral position and
overshoots.
[0054] The process of changing the steering reaction force
corresponds to the hands-off/hands-on states. In consideration of
this problem, for the vehicle steering controller in the first
embodiment, the steering reaction force torque corresponding to the
road surface reaction force is reduced in the hands-on state as
compared with that in the hands-off state, so that the problem is
solved.
[0055] FIG. 9(a) shows the steering reaction force torque with
respect to the steering angle in the hands-on state, and FIG. 9(b)
shows the steering reaction force torque with respect to the
steering angle in the hands-off state. In the hands-on state, road
surface reaction force gain Kf is set to the High value, so that
even if the steering wheel is in return state, the steering
reaction force torque can still be transmitted to the driver
corresponding to the steering angle.
[0056] On the other hand, in the hands-off state, because road
surface reaction force gain Kf is set at the Low value, steering
reaction force Kf.times.F corresponding to road surface reaction
force F is smaller than that in the hands-on state. As a result,
the steering reaction force torque corresponding to the steering
angle in the hands-off state becomes smaller than that in the
hands-on state. As shown in FIG. 10, because it is possible to
prevent the generation of overshoot after the driver's hands are
removed from the steering wheel, the time that the hands are
removed, convergence of the yaw rate, lateral acceleration, or
other vehicle state value changes can be made shorter than that in
the related art (convergence time 2s).
[0057] Process of changing the steering reaction force corresponds
to the steering torque. In the first embodiment, in the hands-on
state, the steering reaction force torque is larger when the
steering torque is larger. Consequently, in switching between the
hands-off state and hands-on state, D is changed smoothly instead
of stepwise between the Low value and High value of coefficient Kf,
so that it is possible to realize both a more natural steering
wheel recovery performance and a good transmission of the road
surface feel.
[0058] For the vehicle steering controller in first embodiment, the
following effects can be realized. Because the device has a turning
unit 3 that is mechanically separated from the steering unit 1,
which receives the steering input, and the steered road wheels 16,
16' corresponding to the steering input, the reaction force motor 5
that applies a steering reaction force corresponding to the turning
state of turning unit 3 with respect to steering unit 1, a
hands-off detection means that detects whether steering unit 1 is
in the hands-off state, and a steering reaction force correction
means that reduces the steering reaction force with respect to that
in the hands-on state. Consequently, it is possible to realize both
an appropriate recovery in the hands-off state and reliable
transmission of the road surface feel to the driver in the hands-on
state.
[0059] The system has torque sensors 12 that detect road surface
reaction force F, and reaction force motor 5 applies steering
reaction force Kf.times.F corresponding to the road surface
reaction force, and when the hands-off state is detected, the
steering reaction force correction means reduces the steering
reaction force corresponding to the road surface reaction force
with Kf set at the Low value. Consequently, in the hands-off state,
an appropriate steering wheel recovery performance is realized,
and, in the hands-on state, the road surface feel can be
transmitted accurately to the driver.
[0060] The controller torque sensors 3 that detect the steering
torque. When the hands-off state is not detected, the steering
reaction force correction means reduces the steering reaction force
corresponding to the road surface reaction force for a smaller
steering torque. Consequently, in switching between the hands-off
and the hands-on state, smooth switching can be realized, and it is
possible to realize both a natural steering wheel recovery
performance and a good transmission of the road surface feel.
[0061] The second embodiment is an example in which the quantity of
reflected steering reaction force torque is changed on the basis of
the steering angle. As the structure of the second embodiment is
the same as that of the first embodiment, it will not be explained
again.
[0062] In the second embodiment, in controller 19, control value Th
of reaction force motor 5 is set on the basis of Equation 3
below.
Th=Kp.times.0+Kd.times.d0/dt+Kdd.times.d.sup.2.theta./dt.sup.2+kf.times.-
F (3)
[0063] FIG. 11 is a flow chart illustrating the process for setting
and controlling the steering angle gain Kp executed by controller
19 in the second embodiment. In steps S1 and S2, the same process
used in steps S1 and S2 of FIG. 2 is performed, so that it will not
be explained again.
[0064] In step S13, because it was determined in step S12 that the
system is not in the hands-off state, steering angle gain Kp is set
at the prescribed High value (corresponding to a steering reaction
force correction means), and it then returns.
[0065] In step S14, because it was determined in step S12 that the
system is in the hands-off state, steering angle gain Kp is set at
the Low value smaller than the High value, and it then returns.
[0066] That is, because steering angle gain Kp is the elastic
moment component for returning steering wheel 6 to the neutral
point (the neutral position), in the hands-off state, it is set at
a smaller value so that there is an appropriate steering wheel
restoration to prevent the steering wheel from exceeding the
neutral point, that is, so that it does not overshoot, while in the
hands-on state, it is set larger to produce an appropriate steering
reaction force torque.
[0067] As another method, one may change Kp.times..theta.
corresponding to the detection value of torque sensors 3 on the
steering wheel side. In this case, on the basis of Equation 4
below, control value Th of reaction force motor 5 is computed.
Th=A.times.Kp.times.0+Kd.times.d.theta./dt+Kdd.times.d.sup.2.theta./dt.s-
up.2+D.times.Kf.times.F (4)
[0068] Here, A is the steering angle coefficient set proportional
to the absolute value of the steering torque. As shown in FIG. 12,
A has a prescribed minimum value in the range of the torque sensor
value corresponding to the hands-off state, and it has a larger
value when the absolute value of the torque sensor value becomes
larger. Also, in order to prevent the steering reaction force
torque from becoming too large, it is set so that when the absolute
value of the torque sensor value exceeds a prescribed level, it
assumes a prescribed maximum value.
[0069] By setting control value Th on the basis of Equation 4,
steering angle coefficient A can be changed smoothly corresponding
to the steering torque. Consequently, it is possible to realize a
more natural steering wheel restoration and an appropriate steering
reaction force torque. Also, when steering wheel 6 does not return
to the neutral position after return of the steering angle, one may
increase Kp.
[0070] As explained in the first embodiment, by reducing elastic
reaction force Kp in the hands-off state, it is possible to reduce
the overshoot in steering wheel recovery and to improve the
converging property of the vehicle behavior. Also, when the
restoration force is insufficient and steering wheel 6 does not
return to the neutral point, with a residual steering angle
remaining, it is possible to increase Kp in order to reduce the
residual steering angle.
[0071] For the vehicle steering controller in the second
embodiment, in addition to effect of the first embodiment, it has
the following effects.
[0072] The system has steering angle sensor 1 that detects steering
angle .theta.. The reaction force motor 5 applies steering reaction
force Kp.times..theta. corresponding to steering angle .theta..
When the hands-off state is detected, steering reaction force
correction means reduces steering reaction force Kp.times..theta.
corresponding to steering angle .theta.. Consequently, it is
possible to reduce the overshoot in the hands-off state and to
improve the converging performance of the vehicle behavior.
[0073] The third embodiment is an example illustrating the change
in the steering reaction force torque reflection quantity on the
basis of the steering angle acceleration in the hands-off state.
The structure of the third embodiment is the same as that of the
first embodiment, so that it will not be explained again.
[0074] In the third embodiment, in Equation 1 for setting the
control value of reaction force motor 5, steering angle
acceleration gain Kdd is changed between the hands-off state and
the hands-on state. In the hands-on state, steering angle
acceleration gain Kdd is set at prescribed value High, and, in the
hands-off state, steering angle acceleration gain Kdd is set at the
Low value smaller than the High value.
[0075] That is, Kdd is the inertial torque component. The smaller
the value of Kdd, the higher the converging frequency of steering
wheel 6. Consequently, the value of Kdd is smaller so that there is
an appropriate steering wheel restoration in the hands-off state,
and the value of Kdd is set larger so that there is an appropriate
steering inertial feel in the hands-on state.
[0076] As another method, one may also adopt a scheme in which
Kdd.times.d.sup.2.theta./dt.sup.2 changes corresponding to the
value detected by torque sensors 3, 3 on the steering wheel side.
In this case, control value Th of reaction force motor 5 is
computed on the basis of Equation 5 below.
Th=A.times.Kp.times..theta.+Kd.times.d.theta./dt+C.times.Kdd.times.d.sup-
.2.theta./dt.sup.2+D.times.Kf.times.F (5)
[0077] Here, C represents the steering angle acceleration
coefficient set proportional to the absolute value of the steering
torque. As shown in FIG. 12, steering angle acceleration
coefficient C is a prescribed minimum value in the range of the
torque sensor corresponding to the hands-off state. In the hands-on
state, the larger the absolute value of the torque sensor value,
the larger the value of C. Also, in order to prevent the steering
reaction force torque from becoming too large, it is set such that
it has a prescribed maximum value when the absolute value of the
torque sensor value exceeds a prescribed level.
[0078] By setting control value Th on the basis of Equation 5, it
is possible to change steering angle acceleration coefficient C
smoothly corresponding to the steering torque, so that it is
possible to realize a more natural steering wheel recovery
performance and appropriate steering reaction force torque.
[0079] For the vehicle steering controller in the third embodiment,
in addition to effect of the first embodiment, the following
effects can be realized.
[0080] The controller of the third embodiment has a steering angle
acceleration detection means that detects the steering angle
acceleration. The reaction force motor 5 applies steering reaction
force kdd.times.d.sup.2t/dt.sup.2 corresponding to steering angle
acceleration d.sup.2t/dt.sup.2. When the steering reaction force
correction means detects the hands-off state, steering reaction
force kdd.times.d.sup.2t/dt.sup.2 is made smaller corresponding to
steering angle acceleration d.sup.2t/dt.sup.2. As a result, in the
hands-off state, the converging frequency of steering wheel 6
becomes higher, and the converging performance can be improved.
[0081] The fourth embodiment is an example in which the steering
reaction force torque reflection quantity is changed on the basis
of the steering angle velocity in the hands-off state. Also, since
the structure of the fourth embodiment is the same as that of the
first embodiment, it will not be explained again.
[0082] In the fourth embodiment, in Equation 1 for setting the
control value of reaction force motor 5, steering angle velocity
gain Kd is changed between the hands-off state and the hands-on
state. In the hands-on state, steering angle velocity gain Kd is
set at the prescribed High value, and in the hands-off state,
steering angle velocity gain Kd is set at the Low value, smaller
than the High value.
[0083] That is, Kd represents the viscous torque component. The
larger this component, the higher the converging damping of
steering wheel 6 in the hands-off state. Consequently, in the
hands-off state, the value is set larger to have an appropriate
steering wheel recovery performance. In the hands-on state, the
value is set smaller to have an appropriate steering viscous
feel.
[0084] As another method, Kd.times.d.theta./dt may be changed
corresponding to the value detected by torque sensors 3 on the
steering wheel side. In this case, control value Th of reaction
force motor 5 is computed with following Equation 6.
Th=A.times.Kp.times..theta.+B.times.Kd.times.d.theta./dt+C.times.Kdd.tim-
es.d.sup.2.theta./dt.sup.2+D.times.Kf.times.F (6)
[0085] Here, B represents the steering angle velocity coefficient
set proportional to the absolute value of the steering torque. As
shown in FIG. 13, steering angle velocity coefficient B is set such
that it has a prescribed minimum value in the range of the torque
sensor value corresponding to the hands-off state, and it has a
larger value when the absolute value of the torque sensor value
becomes larger in the hands-on state. Also, in order to prevent the
steering reaction force torque from becoming too large, when the
absolute value of the torque sensor value exceeds a prescribed
level, it takes on a prescribed maximum value.
[0086] By setting control value Th on the basis of Equation 6,
steering angle velocity coefficient B is changed smoothly
corresponding to the steering torque, and it is possible to realize
a more natural steering wheel recovery performance and an
appropriate steering torque. Also, in Equation 6, in order to have
steering angle .theta. in the reducing direction in the hands-off
state, the second term on the right-hand side is opposite in sign
to the other terms.
[0087] For the vehicle steering controller in the fourth
embodiment, in addition to effect 1 in the first embodiment, the
following effects can be realized.
[0088] There is steering angle velocity detection means that
detects steering angle velocity d.theta./dt, and reaction force
motor 5 applies steering reaction force Kd.times.d.theta./dt
corresponding to steering angle velocity d.theta./dt, and when the
hands-off state is detected, steering reaction force correction
means reduces the steering reaction force corresponding to steering
angle velocity d.theta./dt, so that in the hands-off state, it is
possible to increase the converging damping of steering wheel 6 and
to improve the convergence performance.
[0089] In the foregoing, preferred embodiments of the present
invention were explained. However, the present invention is not
limited to the embodiments 1-4. As long as the essence of the
invention is observed, changes may be made to the design of the
present invention.
[0090] This application is based on Japanese Patent Application No.
2004-361986, filed Dec. 14, 2004 in the Japanese Patent Office, the
entire contents of which are hereby incorporated by reference.
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